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FI~l>il>tQ( inl!lmbran~ 'in~thQ(:f
(1) Configuration
The resistor membrane N-key rollover circuit consists of: '
CD a membrane switch that has the resistor matrix (printed),
®
scan circuit that) convert the unsele.qted, row to
g~~und level,
and,,,
@
comparator
that recognizes
the receive signal leVeL
Matrix
resistors
A
B
Fig.2 R'esistor membraine N-key configuration
(2) Operation
VIN
~can
pulse SP
.
.
.
Receive signal
RIA
:
RS1
SP
lA
II!l<
RS1
:
_ : " : ~ . ~ _ : 1 - · _ · · _ · · _ : , , ; ' : ~ , , : - · ~ _ 1 ~ - 1 : : ' _ , , _ " _ " _ ' ' ' ' ~ ~ ' ' ' 2 , - l i - _ ' ~ _
¢
l;,'~"';r :";~S2
""
2~h
Equivalent
Theoretical A
-{T~
circuit
drawing _ _ _ _ _ _ _ _ _ _ _ _
-==~
____
__1
Fig.3 Theoretical drawing
(2)-1 Removal of phantom key by line separation
Each key switch constitutes a serial matrix resistors RA 1-R2B.
Using those resistors, the not selected
by
the scan pulse is set to
ground level.
This way, line is isolated in terms of circuits (see Fig.3 Equivalent
circuit).
So, there would be no phantom key generated caused by line to
line interference as seen in the conventional configuration.
(2)-2 Receive Signal level recognition
With this method, there would be no generation of phantom key
caused by line to line interference.
But, if there was a rollover operation in the same line of the matrix,
the scan pulse peak value VIN is divided by the matrix resistors
R1A and R1 B to decrease the receive level.
So, the comparator KM1 (KM2) is used to recognize the level.
• So, if assumed that occurrence of comparator threshold value Vref
as many as the maximum rows of the matrix rows, the N-key
rollover can be attained by setting it to the minimum receive level.
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